Niobium halide clusters

B. Peric, R. Gautier, C.J. Pickard, M. Bosiocic, M.S. Grbic, M. Pozek, Solid-state NMR/NQR and first-principles study of two niobium halide cluster compounds. Solid State Nucl. Magn. Reson. 59—60 (2014) 20—30. 

A growing chemistry of niobium oxide clusters continues to emerge. The reduced niobates and the NbO suboxide are also built up from condensation of Me units through shared vertices, namely, Nb60i2. Although the inner halides within the [MeXi2] + core are relatively inert to substitution, Nbe and Tae oxohalides, such as [Nb6Cli2-mOm]"+ m = 1 —4) and... 

Redox Chemistry of the Group 5 Clusters Ligand Substitution Electronic and Molecular Structure Niobium Iodide Clusters NbJJ"-Materials Chemistry Derived from Soluble Metal Halide Clusters A. Higher Nuclearity Clusters Supported Cluster Materials Charge-Transfer Salt Complexes Extended Solids Chemically Modified Surfaces... 

The alkali metal rhenium- and technetium chalcogenide clusters described in Section 5.6 are also octahedral.These clusters have M6Es units with eight face-capping anions on the octahedral faces in contrast to the niobium halide or oxide clusters. The A4M6S14 (A = alkali metal, M — Re, Tc), Cs6Rc6Si2, and... 

Ligand Exchange in Metal Halide Clusters. Rhenium, molybdenum, tantalum and niobium halides are high-valence metal clusters that formally behave as Lewis acids towards halide ions forming anionic complexes that retain the structure of the original cluster. 

A variety of polynuclear cations other than the Alj 3 Keggin ion have been used to pillar clays. Among them, we cite the zirconium tetramer [30,40,41,50,51], chromia polymers [52], bismuth [53], silicon [54], and niobium and tantalum halide clusters [55]. Of these, the most thoroughly studied have been zirconium polymers. 

The known halides of vanadium, niobium and tantalum, are listed in Table 22.6. These are illustrative of the trends within this group which have already been alluded to. Vanadium(V) is only represented at present by the fluoride, and even vanadium(IV) does not form the iodide, though all the halides of vanadium(III) and vanadium(II) are known. Niobium and tantalum, on the other hand, form all the halides in the high oxidation state, and are in fact unique (apart only from protactinium) in forming pentaiodides. However in the -t-4 state, tantalum fails to form a fluoride and neither metal produces a trifluoride. In still lower oxidation states, niobium and tantalum give a number of (frequently nonstoichiometric) cluster compounds which can be considered to involve fragments of the metal lattice. 

Just as, in Group VB, niobium, so, in this Group, molybdenum provides most of the examples of the chalcogenide halides. The occurrence and preparation of such compounds are described in numerous publications. In most cases, they have been obtained as powders, with the composition based on chemical analyses only. The presence of defined, homogeneous phases is, therefore, in many cases doubtful. In addition, some published results are contradictory. A decision is possible where a complete structure analysis has been made. As will be shown later, the formation of metal-metal bonds (so-called clusters), as in the case of niobium, is the most characteristic building-principle. Such clusters... 

The octahedral metal clusters that have long been familiar features of the lower halide chemistry of niobium, tantalum, molybdenum, and tungsten represent a category of cluster different from those so far considered in that their metal-metal bonding is best treated as involving four AO s on each metal 49, 133,144,165,178). 

The lower halides of niobium and tantalum consist of tightly bound clusters of metal atoms, with metal-metal distances close to those found in the metal. They contain ions with average oxidation numbers between +III and +1 (Table 43). Their size depends on the valence electron concentrations (VEC) that are available on the metal atoms for M—M bonding, and on the halide-metal ratio.644 Several reviews have been devoted to the clusters of early transition metals.3,643... 

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